How to Waterproof a Shower with Schluter KERDI
Install a Schluter-KERDI shower tray, curb, drain, and wall membrane using unmodified thin-set mortar to create a 100% watertight enclosure ready for tile.
- Read the tools, materials, safety notes, and steps below for free.
- Tap Start Camera Coach when you want hands-free voice help.
- Allow camera and microphone. Point your phone at the work; the coach watches your progress and tells you the next step.
🧰 Required Tools & Equipment
- ✓ 1/4" x 3/16" V-notch trowel
- ✓ 1/4" x 3/8" square-notch trowel
- ✓ Drywall taping knife or smooth plastic trowel
- ✓ Mixing drill with paddle
- ✓ Utility knife with fresh blades
- ✓ 2-foot spirit level
- ✓ Clean bucket and sponge
📦 Materials & Supplies
- ✓ Schluter-KERDI-SHOWER-KIT
- ✓ Schluter SET or unmodified thin-set mortar
- ✓ Clean water
- ✓ ABS or PVC transition cement (for drain connection)
⚠️ Safety Checkpoints & Warnings
- • Wear an N95 dust mask and eye protection whenever mixing dry thin-set mortar powder.
- • Wear cut-resistant gloves when cutting membrane rolls and trimming around flange contours with a utility knife.
- • Ensure adequate ventilation in the shower area when solvent welding the drain base to plumbing.
📋 Step-by-Step Guide (6 Steps)
Dry-Fit Subfloor Cutout and Drain Assembly
Check that the subfloor is level, clean, and structurally sound. Cut a 4-1/2-inch hole in the subfloor for the drain flange and dry-fit the shower tray and drain assembly without mortar to ensure flush alignment with the waste pipe.
- • The foam shower tray sits completely flat against the subfloor with no rock or wobble.
- • The drain flange drops cleanly into the floor hole centered on the ABS/PVC plumbing.
- • Failing to clean wood debris or drywall dust off the subfloor before dry-fitting.
- • Cutting the subfloor hole too small, causing the drain flange collar to bind and sit above the floor plane.
Install Drain Flange and Bed the Shower Tray
Connect the drain flange to the waste line according to plumbing code. Mix unmodified thin-set mortar to a creamy consistency, comb it across the subfloor using a 1/4" x 3/8" square-notch trowel, then firmly press and walk the foam tray into place to collapse all mortar ridges.
- • Even thin-set squeeze-out visible along the perimeter edges of the tray.
- • Level reads dead-level across the flat perimeter rim while showing slope toward the center drain.
- • Mixing thin-set too dry, preventing 100% continuous contact beneath the foam tray.
- • Using modified thin-set over wood or under impermeable foam where it cannot cure properly.
Adhere the Shower Curb
Measure the shower opening and cut the foam curb to length using a hand saw or utility knife. Apply thin-set mortar to the subfloor and abutting wall surfaces using the square-notch trowel, set the curb, and press firmly downward and back against the tray edge.
- • Curb top is level across its length with a slight inward pitch toward the shower pan.
- • No visible gap between the bottom front lip of the tray and the inside face of the curb.
- • Pitching the top of the curb outward into the bathroom instead of inward toward the drain.
- • Leaving a void between the curb end and the drywall/stud wall.
Embed KERDI Wall Membrane Sheets
Pre-cut KERDI sheet membrane to wall height. Apply unmodified thin-set to the substrate with a 1/4" x 3/16" V-notch trowel, press the membrane into the wet mortar, and smooth it from the center outward using a taping knife to fully embed the fleece backing and remove air pockets.
- • Smooth, flat orange membrane with zero bubbling, wrinkling, or hollow blisters.
- • Mortar fleece impression visible through the surface with no dry spots behind the sheet.
- • Letting thin-set skin over on the wall before hanging the sheet.
- • Pressing too hard with a sharp metal drywall knife and slicing through the waterproofing membrane.
Seal Seams and Corners with KERDI-BAND
Apply thin-set mortar over all vertical/horizontal wall seams, tray-to-wall transitions, and the curb using the V-notch trowel. Embed preformed KERDI-KERECK inside and outside corners, followed by 5-inch KERDI-BAND strips, maintaining a strict 2-inch minimum overlap across all joints.
- • All corner transitions and joints covered by KERDI-BAND with at least 2 inches of overlap beyond every seam.
- • Excess thin-set squeezed out flat and wiped clean with a sponge, leaving no thick buildup ridges.
- • Overlapping seams by less than the required 2-inch minimum waterproof threshold.
- • Leaving thick buildup of mortar at 3-way corners, which causes tiles to kick out later.
Install Pipe Seals and Drain Flange Collar
Comb thin-set around the mixing valve and showerhead pipe nipples, then slide KERDI-SEAL-PS and KERDI-SEAL-MV over the pipes and embed them flat. Bed the circular KERDI drain collar over the integrated bonding flange, troweling flat from the center out to the tray.
- • Rubber gaskets fit snugly around pipe stubs with no tears or gaps.
- • Circular KERDI collar seamlessly integrated into the tray membrane with continuous thin-set bond.
- • Omitting the rubberized pipe collars and relying solely on thin-set or silicone around rough-in pipes.
- • Trapping thick mortar pockets under the drain collar ring that raise the tile height near the grate.
Credit: inspired by an original tutorial by Schluter-Systems North America / Amérique du Nord — watch the original on YouTube.
Don’t have everything?
- No Drywall taping knife? Schluter-KERDI-TROWEL flat side or stiff plastic putty knife
- No Schluter SET mortar? Any ANSI A118.1 compliant unmodified thin-set mortar